Research in our laboratory has been directed towards examining the properties of tRNA methyltransferases purified from rat mammary tumors. Our project is designed to define the characteristics of the tumor methyltransferases and to explore the relationship between altered methylating activity and tRNA methylation in neoplastic tissues. We are: (1)\studying the factors leading to diminished tRNA methylation at selected sites in tumors; (2)\comparing the structural and functional characteristics of purified tRNA methyltransferases from tumors and their normal counterparts; (3)\examining the relationship between methylation and processing of precursor tRNAs; and (4)\developing systems for producing antibodies to purified eucaryotic tRNA methyltransferases.